Electro-hydraulic forming apparatus



Dec. 19, 1967 R. J. BRr-:JCHA ETAL 3,358,487

ELECTRO- HYDRAULI C FORMING APPARATUS Original Filed Dec. 28, 1961 4Sheets-Sheet l 1 ZZ l )7 j! 52 l if! 2% gg' j 1i HIL- z5 21 2a J l -5/sf \2/ 25/ L30 /0 Dec. 19, 1967 R. J. BRI-:JCHA ETAL 3,358,487

ELECTRO-HYDRAULIC FORMING APPARATUS Original Filed Deo. 28, 1961 4Sheets-Sheet 2 f4' if; 4'/

i/ /T Tf I if l' 4/4/ E 1" l. ,Il i a .I l 74 Z3' i ff 7? 7j'I mi 7/fvvf/vra/as Arra/e/vfy Dec. 19, 1967 R. J. BREJCHA ETAL 3,358,487

ELECTRO -HYDRAULI C FORMING APPARATUS Original Filed Dec. 28, 1961 4Sheets-Sheet 3 QQLN Dec. 19, 1967 R. J. BREJCHA ETAL. 3,358,487

y v ELECTRO-HYDRAULIC FORMING APPARATUS Original Filed DeC. 28, 1961 4Sheets-Sheet 4 mnm I ATTORNEY United States Patent O 2 Claims. (Cl.72-56) This application is a division of my co-pending application Ser.No. 162,790 filed Dec. 28, 1961, and now Patent No. 3,222,902.

This invention relates to a method and apparatus for shaping workpiecesof deformable material. More speciiically, it pertains to the forming orshaping of a blank of sheet metal and the like by the utilization of thehigh energy of an electrical discharge in a hydraulic medium. Theinvention lends itself particularly to the forming and/ or shaping oftubular container -bodies and the like in high speed production.

The term electro-hydraulic as used herein designates the concept ofreleasing electrical energy in a contained hydraulic environment. Thistechnique may be thought of as direct conversion of electrical energyinto mechanical energy in that the high energy shock waves generated inthe hydraulic medium by the rapid discharge of a high mtensity sparkprovides an energy front for performing work. Normally, the hydraulicmedium is a suitable incompressible fluid and the spark producing meansis a pair of spaced electrodes immersed in the fluid. Electrical energyrapidly released from a high energy storage source, such as a bank ofcapacitors, is discharged across the spaced electrodes. The reaction ofthis spark discharge in the electrode gap creates tremendous pressurebuild-ups in the surrounding duid which transmits the resulting shockwaves toward a workpiece suitably mounted to a support or forming die.

l:`.lectrohydraulic forming has many advantages over processes usedheretofore. Conventional mechanical forming, for example, is limited toa narrow range of shapes and patterns.

Special tooling and involved procedure is required to form workpieces ofcomplicated geometry, and mechanical forming is additionally limited tothe pressure levels of available forming presses. Electro-hydraulicforming is more versatile than mechanical forming since an almostinfinite variety of ditiicult configurations may be formed in a singleoperation. Moreover, the range of Working pressures available with anelectro-hydraulic process are far greater than in mechanical forming. Byincreasing the capacity of the energy storage source, almost unlimitedamounts of energy can be released to produce working pressures severaltimes that of conventional presses. This energy may be used to form,weld and pierce workpieces all in one operation, if desired.

Another disadvantage of conventional forming methods is the deleteriousresults often achieved in the physical properties of the workpieces.Uneven forming pressures cause creep, irregular thinning and adversestressing in many instances where extraordinary drawing of theworkpieces is required. This problem is even more acute when materialswhich do not readily lend themselves to conventional forming practicesare used. For example, certain alloys and high tensile strengthmaterials used in industry today are known to be diicult to work. Thetendency of these materials to fracture when worked with conventionaltools and the requirement of extremely large presses to accomplishsatisfactory results have seriously limited the use of these materialsfor many applications. The high and continuous pressure distributionsachievable in electro-hydraulic forming makes this process well s-uitedfor these more diiiicult jobs.

Attempts to overcome the problems of conventional forming by devisinghydraulic forming and explosive forming techniques have not beenentirely satisfactory. In hydraulic forming, where working pressures areapplied externally to a hydraulic medium and transmitted uniformlythrough the medium to a workpiece, the problems reside in therequirement of presses of excessive size to provide the necessarypressures and in the slowness of the operation. In explosive forming,high pressures are achievable but the process is slow and oftenextremely dangerous since it does not lend itself well to automation.Moreover, explosive forming is noisy and therefore objectionable in highspeed manufacturing operations.

It has been found that many of the shortcomings of these known formingprocesses can be overcome with the electro-hydraulic technique, since itlends itself Well to equipment designed for high-speed, versatileoperation and maximum safety.

An important object, therefore, of this invention is to overcome theproblems of forming workpieces which are not readily worked by knownprocesses.

Another object of this invention is to provide a method for formingWorkpieces electro-hydraulically.

Another object of this invention is to provide a method for shapingdeformable workpieces electro-hydraulically with a forming head which isself contained and adapted for high speed operation.

Another object of this invention is to provide a method for shapingtubular container bodies to the contour of a forming dieelectro-hydraulically with a self contained fluid filled forming headadapted for high speed operation without the necessity of filling andemptying the tluid before and after each forming operation.

A further object of this invention is to provide a forming head forelectro-hydraulically forming workpieces.

Another object of this invention is to provide an electro-hydraulicforming head which is self contained and adapted for high-speed formingoperation.

Another object of this invention is to provide an electro-hydraulicforming head adapted to shape tubular container bodies to the contour ofa forming die.

Still another object of this invention is to provide high speedapparatus for electro-hydraulically forming Workpieces sequentially.

Yet another object of this invention is to provide an apparatus forelectro-hydraulically shaping successively fed container bodies to aforming die.

Numerous other objects and advantages of the invention will be apparentas it is better understood from the following description, which, takenin connection with the accompanying drawings, discloses a preferredernbodiment thereof.

To accomplish these and other objects of this invention, there isprovided an electro-hydraulic forming head cornprising spaced electrodesimmersed in an incompressible il'uid which is contained within adiaphragm member of elastomeric material. The forming head is positionedover the workpiece with the resilient diaphragm disposed substantiallyin contiguous relation with the surface of the workpiece. The rapiddischarge of electrical energy within the immersing fluid createshigh-pressure shock waves which move outwardly through the fluid toforce the diaphragm against the workpiece. In this manner, the pressurefronts moving with the shock waves are received against the diaphragmand converted to mechanical energy either for shaping the workpieceagainst a die or for performing other work thereon.

3 Referring to the drawings:

FIG. 1 is a sectional view of one form of the invention showing aworkpiece in position before shaping it by the method of this invention.

FIG. 2 is a sectional view showing how the form of the invention in FIG.1 is used to carry out the method of ythis invention.

FIG. 3 is a perspective view of a typical body formed by the practice ofthis invention.

FIG. 4 is a vertical section of a preferred form of machine in which theinvention is embodied.

FIG. 5 is a sectional view taken substantially along lines 5 5 of FIG. 4showing another form of the invention.

FlG. 6 is a perspective view of a container body shaped bythe form ofthe invention of FIG. 5.

FIG. 7 is a sectional view similar to FG. 5 showing still another formof the invention.

FlG. 8 is a perspective view of a container body shaped by the form ofthe invention of FlG. 7.

Referring to FIG. 1, there is shown one embodiment of this inventionwhich may be used for shaping a workpiece or blank 10 of deformablematerial into a dished body 1l of the type shown in FG. 3. The blank 10may be any material capable of permanent deformation; and the inventionhas been used to shape successfully metal blanks, such as tin plate andaluminum, and certain plastic materials, such as polyethylene andpolystyrene. Moreover, it will be understood that the dish-shaped body11 is just one of many configurations capable of being formed by theinvention. Not only may bodies of more complicated geometry be formed bythe practice of this invention, but forming, welding and piercing mayalso be accomplished and all in one operation, if desired. Y

The blank is shown interposed between a die member D and anelectro-hydraulic forming head designated generally as H. The die memberD and head H are moveable relative to each other for interposing andclamping the blank 1t) in forming position therebetween. Die member Dmay be of any desired configuration, but is shown here in simplied formas comprising a female die block 12 carried on a supporting frame 13 andactuatable by a cam i4 engaging a spring-biased lift bar 15. An ejectorpin 16 mounted to frame i3 extends centrally of die block l2 to ejectthe body 11 after the forming operation. Die block 12 is showncontaining a plurality of vent holes 17 extending into the die cavity.The function of these vent holes is to permit evacuation of the airtrapped between the blank and the die block during the formingoperation, as will hereinafter be more fully explained.

It'will be understood that blank 19 can also be free formed without theuse of die member D. For example, in those instances where the formingoperation calls only for bulging the blank into a generally curvilinearcontiguration, a die is unnecessary and only a retaining ring forclamping the blank to the forming head H would be required. This latterpractice may find use in the forming of such items as automobile hubcaps, container ends, dish ware, etc.

The forming head H is a major aspect of this invention and will now bedescribed in detail. It comprises a block member 20 in which a cavity 21has been formed. This cavity is lilled with a hydraulic medium 22,preferably an incompressible liuid. Ordinary tap water has been foundsuitable for many types of forming, but it will be understood that otherhydraulic iiuids may serve just as well. However, in those instanceswhere the operating electrical energy levels are critical, higherefficiencies may be achieved with uids of greater electricalconductivity and ionization characteristics than water.

A pair of electrodes 23 are mounted in the wall of block member 20 ininsulators 24 and extend into the cavity 2l. The electrodes are thusimmersed in the uid 22 within the cavity. The actual number and spacingof electrodes may vary, according to the particular job to In the way ofillustration,

be performed by head H, but in the form shown a single pair having tips25 in opposed spaced relationship constitutes the preferred form of theinvention.

The electrodes may be of any suitable conductor material, such asberyllium copper rod, b'ut a material should be selected having thehighest possible conductive properties as well as ruggedness anddurability. The insulators 24 must also be of a durable material, andTeflon is one such material which has been found especially satisfactoryfor the operating conditions present in electro-hydraulic forming.

The spacing of the electrodes and the geometry of the electrode tipsplay important roles in the invention. The length of the gap betweentips 25 should be suicient to ensure complete formation of the sparkdischarged therebetween and for the formation of uniform wave frontsacross substantially the full width of the cavity 2l. This ensuresmaximum utilization of the available energy released by the discharge.On the other hand, the tip spacing must be less than the distancebetween either tip and the surrounding metal walls of the cavity toavoid shorting to these walls. Any tendency of the electrical charge tojump to these walls disrupts the formation of the wave fronts in fluid22 and lowers the effectiveness of the operation and, in some instances,could ruin the blank 10. Therefore, the Velectrodes 23 must be carefullyspaced to overcome these problems.

Electrode tipV geometry is related to these problems. Experimentationhas indicated that the uniformity of spark discharge and resulting waveformation may vary substantially with changes in tip geometry. It hasbeen found that best results are achieved where the tips are shaped toprevent any tendency of the spark to stray over the surface of theelectrode; i.e., to initiate from rst one point on the electrode tip andthen another. In the form of the invention shown, electrode tips 25 aretapered to a rounded point at their very end. This geometry has beenfound to give effective -control over the shape of the shock Wave formedin the gaseous conductive channel or gap between the electrode tips andtherefore achieves 1glrezter continuity in pressure distribution in theforming The electrodes 23 are connected to the terminals of a highvoltage power supply. The type of electrical circuit used in theinvention is not important, but it will be understood that the powerrating of the electrical source must correspond to the energyrequirements of the forming process. That is, the circuit must becapable of a rapid discharge of energy commensurate with the work tobe-accomplished in any one cycle of operation. Moreover, the

power rating of the electrical source is directly related to the rate ofoperation. In other words, forming rate in terms of available chargingtime and rate of spark dis- Y charge are variables in the determinationof the rating of the power source for a particular job requiring agivenY energy level.

One form of electrical circuit which may be used in the instantinvention is illustrated schematically in FIG. l. The equipment embodiedin this circuit includes a high voltage D-C transformer rectifier powersource P connected to a bank of capacitors designated generally as C.The capacitors constituting bank C may be wired in seriesparallel andmay vary in number, of course, depending upon the total net capacityrequirements of the circuit. the average power requirements forelectro-hydraulically forming small sheet metal container parts at anestimated rate of 500 parts per minute was determined to be 45-60 kw.This determination was based on a three to fourelectrical-discharges-per-cycle operation, with the energy requirementper discharge being approximately 1800 joules. From this, the rate ofvoltage lbuild-up and the necessary charging current can be estimatedfor achieving a final capacitor voltage in the neighborhood of 60 kv.corresponding to the quantity of energy required when stored in acapacitor bank rated at one microfarad. This power requirement is basedon a condition of constant current charging, which is considered to bemost desirable from the standpoint of power supply life and reliability.It will be appreciated that more rapid discharge may be achieved byreducing the capacitance of the storage bank C. This must be accompaniedby an increase iu voltage if the same energy is to be discharged. Itwill be readily understood by those skilled in the art that any numberof capacitance-voltage combinations could be used to achieve the desiredenergy levels and that circuit configurations could be arranged forvarying the capacitance over a substantial range to fulfill differentjob requirements.

Also included in the circuit pair of switches S1 and S2. the capacitorbank C from illustrated in FIG. 1 is a S1 is the switch for charging thepower supply. Once the required capacitor voltage is reached, S1 isopened to isolate bank C, whereupon S2 is closed to release the energystored in the bank across electrodes 23. The charactenstics of S1 arenot critical; but since the strength of the shock waves created by thedischarge across electrodes 23 is dependent upon the rate of energydissipation in the gap, switching losses attributable to S2 must be keptat a minimum to ensure more rapid discharge and higher eiliciences. Thisswitch must have low loss, rapid switching time, and the ability towithstand full voltage during the charging time. Mechanical switches aremuch too slow, of course; therefore, electronic switching is desirable.Types of switches possessing the `desirable characteristics and whichmay be suitable for high speed production equipment include thetriggered spark gap, hydrogen thyratrons, ignitrons, and possiblysolid-state controlled rectiers.

The circuit may also include a resistor R in series with the capacitorbank C. This resistor acts as a current limiter during the charging ofbank C.

A vital part of the forming head H is an elastomeric diaphragm 30 whichis suspended across the open end of cavity 21 and secured in Huid tightengagement with block member 20 by a retaining ring 31. This diaphragmmay be of any impermeable material but is preferably natural rubber or arubber derivative. The functions of rubber diaphragm 30 are several. Itsprimary function is to act as a shock attenuator or, stated differently,to attenuate the adverse shock wave and implosion elfects resulting fromcollapse of the electrical spark at the time of discharge. Experimentsinforming certain workpiece coniigurations have indicated that severeinward buckling occurs locally in the walls of the workpiece instead ofa desired uniform bulging. This has been attributed at least in part tothe collapse or disintegration of the electrical spark in the gaseouschannel between the electrode tips at the time of discharge, creating animplosive condition within the hydraulic uid and tending to cause forcesof brief duration to act on the walls of the workpiece opposite thanwhat is intended. The phenomenon of implosion in electro. hyraulicforming is not yet fully understood, but its adverse effects have beenvirtually eliminated by the use of the rubber attenuator or diaphragm30.

The thickness of the rubber diaphragm used in this invention will vary,depending on the nature of each forming job and the implosion problem tobe corrected. For simple forming operations on thin metal containerparts, diaphragms of one half to three quater inch thickness havedemonstrated satisfactory attenuating results. It will be appreciated,however, that the thickness of the attenuator 30 need not be uniform. Infact, in some instances, it may be desirable to use a diaphragm ofspecial contour to achieve a more uniform shock wave distribution in thefluid.

Diaphragm 3u performs other functions contributing to the success of theinstant invention. It serves as a secondary transmitting medium whichperforms the actual shaping of the blank 10. That is, the energy carriedby shock waves through fluid 22 is converted to mechanical energy by thediaphragm which reacts to the pressure fronts in the fluid to deformblank 10 into a desired shape.

Being mounted over the open end of cavity 21 as shown, diaphragm 3i)also provides a convenient means for containing the fluid within thecavity. This function is of paramount importance from the standpoint offorming rate and safety of the operation. It avoids having to evacuateand refill the cavity with fluid between cycles, which means that theforming head H is essentially selfcontained and capable of cyclicoperation at high rates of speed. Thus, the shortcomings of explosiveforming, as mentioned hereinbefore, is overcome with a simpleconstruction having all the necessary components, including thehydraulic fluid, contained in the one unit. Moreover, the hazard ofdangerous stray currents which could result if the fluid were allowed toleak and short the electrodes to exposed external machine members isentirely eliminated, since diaphragm 30 is impermeable and is sealed influid tight engagement with block member 20 as hereinbefore explained.

Another and no less important function of rubber diaphragm 3G is that ofan insulator for the electrical fields within the forming head H. Itwill be appreciated that in those forming operations where it isdesirable to use a large gap length between electrodes to achievebroader pressure distribution in the fluid, a point is reached wherearcing to the workpiece may occur rather than across the electrodes.Since rubber is an excellent electrical insulator, the presence ofdiaphragm 30 between the electrodes and the workpiece removes anytendency for arcing or shorting to the workpiece.

Another feature of this form of the invention is in the geometry of theclosed end of cavity 2l. As shown in FIG. l, the wall closing the end ofthe cavity may be concave and of a general paraboloidal contour. Thisprovides a reflector surface 32 which, in some instances, may bedesirable to control the formation and propagation of the shock waves influid 22. For example, where the shape of the cavity 21 is such that thewall surfaces dening the cavity interfere with a uniform and symmetricaldistribution of forces throughout the fluid, a portion of this wall maybe appropriately shaped to direct more effectively the forces toward andagainst the workpiece. Reflector surface 32, therefore, is a means forcontrolling the force distribution of the radiatingshock waves in fluid22 and thus bring a maximum amount of the energy released by theelectrical discharge to bear on the workpiece.

Means are shown in FIG. 1 for controlling the supply of fluid 22 withincavity 21. Valve controlled inlet and exit lines 33, 34 communicate withthe cavity and lead to and from a supply reservoir, not shown. Thefunction of these supply lines primarily is to circulate the duid fromtime to time and to maintain a definite volume of fluid in the cavity.This is necessary because after a great many cycles of operation,successive electrical discharges have drastically altered the physicalproperties and raised the temperature of the fluid. These conditions mayadversely affect the efficiency and performance of the forming operationas well as damage the diaphragm 30 and other components of the unit.Therefore, it is desirable that the hydraulic Huid be replaced at leastperiodically or, if desired, a system for continuous recirculation maybe employed.

Having thus described one form of an electro-hydraulic formingapparatus, the process of shaping the blank i0 with this form of theinvention can be comprehended by referring to FIG. 2. Having placedblank 10 in position on forming die D and brought the forming head Hinto clamping position over the blank, switch S2 is closed to releasethe energy stored in capacitor bank C. Instantly a high intensity sparkleaps the gap between electrodes 23, initiating Within Huid 22 highenergy shock waves which move outwardly through the medium and towarddiaphragm 30 disposed immediately above blank 10. As the wave fronts,reach the diaphragm, it yields under the high pressure of the lluid toforce blank 10 into the die cavity.

The result is a dish-shaped article 11 of the type shown in FIG. 3.Thereafter, the die member and forming head are separated to eject thecompleted article from the die (see FIG. l).

As mentioned hereinbefore, it is desirable in those operations using thedie member D to evacuate or vent the air trapped between the blank andthe die cavity. This is so because of the extremely high speed at whichelectro-hydraulic forming takes place. The deformation of the workpieceis so rapid that the dead air in the die cavity cannot escape around thedeformed blank, as in some punch or deep draw forming methods, but istrapped in the cavity and compressed to very high pressures. Thisinterferes with the proper forming of the workpiece tending to cause itto buckle locally away from the die cavity. Unless this compressed `airis removed faster than the build up of pressure in the cavity, irregularand incomplete forming results in thc-se regions of trapped air pockets.Several means may be employed for venting the die cavity. A vacuumsystem for evacuating the cavity may be used, if desirable, but thissystem may have some disadvantages in a high speed forming operation. Inthe form of the invention illustrated in FIGS. l and 2, die evacuationmay be accomplished by venting the die cavity to atmosphere. A pluralityof vent holes 17 may be formed in the die member D in sufficientquantity and distribution to achieve adequate venting. This simpleconstruction has been found satisfactory for forming less complexworkpieces, such as the dish shaped article shown in FIG. 3.V However,where the shape of the workpiece and corresponding die cavity is suchthat venting through vent holes is too slow, as, yfor example, where thepath of the escaping air is more irregular, another form of die ventingmay be more feasible. In such instances, a porous die made of sinterediibre or powder metal may provide a more eicient means for rapidevacuation of the die cavity.

Turning now to FIG. 4, there is illustrated another form of theinvention incorporated in a machine adapted for high speed productionforming of container body blanks. A forming head I-I1 is mounted forreciprocation on a rotating turret 4d. Depending on the production ratedesired of this particular machine, a plurality of heads H1 may bespaced about the turret and carried in supports 41 which operate inslide ways 42 mounted on the turret. Rollers 43 operating in cam track44 mounted on the machine main frame 45 control the reciprocation of theheads H1 in time with rotation of turret 40. The turret is driven inintermittent motion by a suitable drive mechanism, such as a Genevadrive, designated as 46. i

Turret 40 is provided with a table 47 on which is mounted a plurality ofdie members D1 equal in number to the forming heads H1. Each die membercomprises a pair of female die blocks 48, one of which is pivotallymounted to table 47 with a pin 49 (see FIG. 5). The other die block isrigidly bolted to the turret in mating relation with the pivoted dieblock. A roller 50 mounted on a bracket 51 iixed to the pivoted dieblock moves in an annular cam track 52 to open and close the die memberin time with rotation of turret 40.

A feed wheel 53 is rotatably mounted at a feedstation above the path ofthe die members D1. This feed wheel revolves in intermittent registrywith turret 40 to bring a container 4body blank 54 into alignment with adie member D1 at the feed station. Blank 54 may be formed from flatstock with a longitudinal side seam on a conventional can body maker.The strength of the side seam, of course, must be-sufiicient towithstand the forming stresses imparted to the wall of the blank; and ithas been found that lap welded side seams, for example, possess adequatestrengthfor electrohydraulic shaping the blank 54 without any tendencyfor the seam to rupture or fracture when drawn. Simultaneously with thealignment of blank 54 with die member D1, the forming head H1 locatedimmediately above this die member descends to pass 8 through the blank54, stripping it from feed wheel 53 and carrying it downwardly into thedie member D1. The turret 4d is then indexed step by step to a formingstation where the body blank 54 is electro-hydraulically formed to thedesired shape.

The forming station is located on the right hand side of the machine asseen in FIG. 4. The relationship of the machine components at theforming station is best illustrated in FIG. 5, which is a sectional Viewtaken through a portion of the machine at the forming station. In thisview, the container body blank 54 is shown disposed within the diemember D1 with the forming head H1 inserted within the body blank.

The forming head H1 itself comprisesra tubular rubber diaphragm 60mounted to the reciprocable support 41 by means of a retaining nut 61which is threaded into the lower end of support 41. Diaphragm 60 is heldto the support by screws 62 which extend through nut 61 into a ring 63imbedded below the upper end of the diaphragm. An electrode 64 encasedin an insulator 65 extends centrally of support 41 and nut 61 intogripping engagement within the upper end of diaphragm 60.

Another electrode 66 is mounted in gripping engagement within theopposite end of tubular diaphragm 69. This electrode is encased in aninsulator 67 and is held to the diaphragm by bolts 68 which extendthrough the Velectrode andY insulator into another ring 69 imbedded justabove kthe lower end of the diaphragm. A tapered steel guide block 70surrounds the electrode 66 and insulator 67 and is adapted to seatwithin a tapered opening 71 in table 47 to lock the forming head inalignment with'the die member.

A roller contact 72 mounted on a bracket 73 formed integrally withelectrode 66 projects below table 47 to make electrical contact with aconductor 74. Conductor 74 is mounted in a track 75 supported from themachine frame beneath the turret table 47 (see FIG. 4). Conductor 74 isannularly aligned with the indexing path of the turret 40 and, ifdesired, may extend around the axis of the machine to provide electricalcontact at several successive stations for reasons to be hereinafterexplained.

An electrical circuit identical in all respects to the one hereinbeforedescribed is connected across electrode 64 and conductor 74. In thisway, the circuit is completed through roller contact 72 to the oppositeelectrode 66 when the forming head H1 is lowered completely into the diemember D1 with guide block 70 seated firmly within opening 71.

The interior of tubular diaphragm 60 is filled with a hydraulic fluidwhich completely lls the interior cavity between the electrodes andimmerses the tips of the electrodes. As hereinbefore explained, it isoccasionally necessary to circulate the supply of fluid 80 in thediaphragm, and this may be done by supply lines S1 communicating withthe cavity through ports 82 in the retaining nut 61 and passages 83formed in the insulator 65. With the ends Vof diaphragm 60 tightlyengaging nut 61 and guide block 70, respectively, and with the encasedelectrodes 64,V 66 snugly inserted within the ends of the diaphragm, thefluid 80 is sealed Within the diaphragm against escape. The resilienceof the rubber diaphragm ensures a uidtight compartment even afterprolonged operation ofthe forming head.

There is thus illustrated a completely self-contained forming head H1which operates as a unit in a machine adapted for high speed formingoperation. In this form of the invention, the forming head H1 is capableof rapid reciprocation to pick up a container body blank at a feedstation, move inwardly of the blank to strip the blank from the feedmeans, and move the blank downwardly into a die member with the blankappropriately interposed between the forming head diaphragm and the diecavity. With the electrodes and hydraulic duid carried as a unit withthe forming head, forming of the blank may be neatly and safelyaccomplished without time consuming 9 filling of the blank with duid andwithout the attendant danger of splashing and shortcircuiting.

The die cavity in each die member D1 as shown in FIG. 5 is adapted forshaping the container body blank 54 into a generally barrel-shapedconfiguration. The interior Wall of each die block 48 is formed with acurvilinear surface 90 increasing in diameter from each end of the diemember toward the middle. The surface 90 in one die block is, of course,symmetrical with the same surface in the mating die block.

A plurality of inwardly projecting ribs l may be formed in each surface90 as desired, to provide reinforcing or stiener beads 92 in the wall ofthe shaped body, as illustrated by the completed container body shown inFIG. 6. Ribs 91 may be either integrally formed in wall surfaces 90 ormay be in the form of separable inserts which are attached to the wallsof the die cavity. Similar inserts, such as shown at 93, may also beused to form decorative patterns, label and/or identication marks, inthe wall of the container body. Typical of this type of marking in theindented identification mark 94 shown in FIG. 6. As in the case of ribs91, the inserts 93 may also be formed integrally with wall surfaces 90.However, it is preferred that these inserts be separable so as to permitthe use of the same die members for the forming of a wide variety ofsurface configurations. Accordingly, inserts of various patterns may bebolted or otherwise mounted in slots appropriately placed in the wallsof the die cavity` The material of inserts 93, and also that of ribs 91if the latter are in the form of separable inserts, need not necessarilybe as hard and rigid as the die members themselves. Experiments lwithvarious materials for inserts have indicated that satisfactory indentedpatterns may be accomplished with softer materials. Rubber and libreinserts have been used successfully with a high degree of patternclarity. Apparently, the extreme rapidity with which theelectro-hydraulic forming takes place, coupled with the Vfavorablecontinuous pressure distributions present in the forming head, accountsfor the success of these softer insert materials. Notwithstanding thetendency of such inserts to become rounded at the edges as the wall ofthe body blank is deformed thereover, they have been found to hold upvery well after prolonged operation while Vstill providing indentationsof satisfactory depth and clarity. .The obvious advantages of thesesofter materials are that a wider variety of inserts are provided morecheaply than metal inserts, the type or set is more easily formed in theinserts, and the yieldable nature of the softer inserts helps to avoidexcessive stressing of the Wall of the container body as it is drawnover and around the insert type.

Die members D1- are also provided with means (not shown) to evacuate theair trapped in the die cavity. Evacuation may be accomplished either bya vacuum systern or by using vented or porous die blocks, ashereinbefore described. r

Returning now to a description of the operation of the form of theinvention illustrated in FIG. 5, the forming head H1 has descendedentirely through die member D1 so -that the body blank 54 with diaphragm60 therein rests in the die cavity and guide block 70 engages withinopening 71 to lock the parts in alignment. In this position, rollercontact 72 has been lowered into engagement with conductor 75 andpivoted die block 48 is held firmly against fixed die block 48 by roller50 opera-ting in track 51. By a suitable control means (not shown), S1is opened and S2 closed to lrelease the electrical charge stored incapacitor bank C.

The energy released by the resulting discharge across electrodes 64, 65is transmitted by the shock waves thus created in uid 80 outwardlyagainst tubular diaphragm 60. The diaphragm instantly expands under theiniiuence of the tremendous pressures within to deform body blank 54 tothe contour of surfaces 90. Thereafter, head H1 is withdrawn from thedie member and hinged die block 48 is swung away to expose the completedbody, which may then be ejected from the die member by a suitableejector means (not shown).

In the event that more than one discharge of electrical energy isnecessary or desired in the forming operation, the means for Controllingthe operation of switches S1 and S2 can be synchronized with the turretdrive to effect successive discharges. If desired, these successivedischarges may all occur while the turret is at one position or station.However, the time required for operating the switches and charging thecapacitor bank C after each discharge would drastically reduce the speedof the machine if all discharges are accomplished at one fixed station,Higher speeds and more efficient distribution of switching and chargingtime are achieved by providing that the successive discharges take placeduring the interval the turret is being indexed from one station to thenext. That is, the speed of the machine may be regula-ted so that thedesired number of discharges takes place during the interval of timethat the turret moves between stations. The only requirement is that theconductor 74 extend for at least the same annular distance betweenstations so that a complete circuit is maintained for as long as ittakes the turret to move this distance. For this reason, conductor 74 isshown in FIG. 4 as extending at least a considerable distance around themachine in direct alignment below the path of the turret. Thus, as theturret .rotates the roller contact 72 maintains electrical contact withconductor 74 for as long as necessary to release the desired number ofdischarges in head H1.

It will be understood that the energy released in each successivedischarge of the electrodes may be adjusted to any desired magnitude bymeans of appropriate circuit controls synchronized with the rotation ofthe machine. In this manner, the energy of each succeeding discharge maybe raised or lowered, as desired, depending on the nature of thespecific forming operation. For example, the most eicient forming cyclefor a particular container body may call for three or four successivedischarges of diminishing energy magnitude, in which case the controlcircuit may be arranged so as to adjust the voltage level of thecapacitor bank C at appropriate intervals in the forming cycle.

Referring now to FIG. 7, there is shown another form of the inventionwhich is specifically adapted for reshaping drawn container body blanksclosed at one end. There is shown a forming head H" which is identicalin all respects to head H1, just described, except for the lowermostelectrode. Since the bottom end of the drawn body blank 160 is closed,usually in the form of a recessed or concave end panel 101, whichprevents moving the forming head completely through the body blank aswith the open-ended body blanks illustrated in FIG. 5 anotherarrangement is needed for bringing the lower electrode in the forminghead into circuit. In the arrangement shown, a lower electrode 102 issecured in the lower end of the tubular diaphragm by an integral lip 103imbedded in the diaphragm. The lower surface 104 of the electrode iscontoured to conform substantially to the interior surface of the endpanel of body blank 100.

A contact element 105 having a rounded head portion 105 is mounted totable 47 of the turret in axial alignment with head H". The uppersurface 107 of head portion 106 is contoured to conform substantially tothe exterior surface of the end panel of the body blank. Elernent 105 isslidably encased in a well in an insulator housing 108 which in turn isbolted to turret table 47. The upper surface of the insulator housingsurrounding head portion 105 is recessed to accommodate the lower end ofbody blank 100. A coil spring 109 surrounding the contact element 105 inthe well biases the element upwardly into pressed engagement with theend panel of body blank 100. Electrical contact is thus made from theupper contoured surface of head portion 106 through the 1 1 end panel101 to the lower contoured surface 104 of electrode 102. A rollercontact 110 similar to that carried by forming head H1, describedhereinbefore, is mounted to the lower end of contact element 105 on abracket 111 to make electrical ycontact with conductor 74.

In operation, forming head H descends into body blank 100 to strip itfrom the feed means and carry it into the die cavity. As the blankdescends through the die cavity, it depresses contact element 105against the pressure of spring 109 and comes to rest against insulatorhousing 107. Due to the action of spring 109, element 105 is held lrmlyagainst lthe end panel 101 to ensure good electrical contact. At thispoint, the `control means operating switches S1 and S2 energizes thecircuit to discharge the electrodes. The spark initiation and resultingshock waves is in all respects identical, of course, to that describedin connection with forming head H1.

The resulting container body illustrated in FIGURE 8 is typical of themany configurations which may be formed in this manner from drawn bodyblanks. It will be understood, of course, that in the practice of thisform of the invention, the container itself must be of an electricallyconductive material. Drawn steel or aluminum bodies are typically suitedfor this operation. However, drawn bodies of plastic or othernon-conductive material could also be formed in this manner if the endpanel 101 were pierced or otherwise altered to obtain electrical contactbetween electrode 102 and contact element 106. An example of a drawncontainer body of non-conductive material which might be suitable forthis type of forming is that used in gas-propelled dispensingcontainers, where the closed end panel is conventionally pierced toallow insertion of a propellant and thereafter plugged with a rubberstopper or the like. In this type of drawn body, the gas hole wouldconveniently accommodate a contact element 106 tailored to t through thehole to make electrical contact with electrode 102.

It is thought that the invention and Imany of its attendant advantageswill be understood from the foregoing description and it will beapparent that various changes may be made in the form, construction, andarrangement of parts of the apparatus mentioned herein and in the stepsand their order of accomplishment of the process described herein,without departing from the spirit and scope of the invention orsacrificing all of its material advantages, the apparatus and processhereinbefore described being merely a preferred embodiment thereof.

We claim:

1. A forming head mechanism for electro-hydraulically shaping a drawncup-shaped container body in a forming die comprising a support, `atubular impermeable rubber diaphragm secured at one end to said supportin fluid tight engagement, said diaphragm having exterior geometrysubstantially the same as the interior of said body and being insertibletherein, a pair of electrodes tightly inserted within the opposite endsof said diaphragm with their tips projecting inwardly of said ends inpredetermined spaced ali-gnment, one of said electrodes extendingthrough said support and the other being secured in uid tight engagementto the opposite end of said diaphragm, said other electrode having anexterior contacting face contoured to conform substantially to theclosed end of said cup-shaped body when said diaphragm is insertedtherein to make electrical contact through said end panel with theconductor of an electrical power source adapted to be contacted with theexterior surface of said end panel, a hydraulic iluid contained withinsaid diaphragm im'- mersing said electrode tips, and a conductor leadingfrom said one electrode externally of said diaphragm adapted to beconnected to said power source to complete an electrical circuit throughsaid electrodes for discharging electrical energy across said electrodetips whereby shock waves are created within said fluid which propagateoutwardly and expand said diaphragm to shape said body to the contour ofsaid die. Y

2. An apparatus for electro-hydraulically shaping drawn tubularcontainer body blanks having closed bottom ends comprising a die memberhaving an open-ended cavity for receiving said blanks one at a time; aforming member movable relative to and within said die member forinterposing a body blank therebetween, said forming member including atubular impermeable elastomeric diaphragm of exterior geometrysubstantially the same as the interior of said body blank and beinginsertible therein, a hydraulic medium contained within said diaphragm,and a pair of spaced electrodes inserted within opposite ends of saiddiaphragm with their tips immersed in said medium in predeterminedspaced alignment, one of said electrodes having a contact externally ofsaid diaphragm adapted to extend beyond the end of said blank when saidYdiaphragm is inserted therein and the other of said electrodes having anexterior surface contoured to conform substantially to the closed bottomend of said blank', a first conductor of an electrical power sourcespaced from said die member and engageable With said contact ofV saidone electrode; a second conductor of said power source disposed adjacentone end of said cavity opposite said first conductor and adapted toengage said closed bottom end when said blank is within said die cavity;and control means for bringing said electrodes into circuit with saidpower source through said contact and first conductor and through saidsecond conductor and closed bottom end for discharging electrical energyacross said electrode tips whereby high pressure shock waves are createdin said medium which transmit energy outwardly to expand said diaphragmand shape said blank to said cavity.

References Cited UNITED STATES PATENTS 2,559,227 7/1951 Rieber 72-56OTHER REFERENCES Explosives From Space Age Shapes; published in Steel,August 25, 1958, pp. 82-86.

RrCHARD I. HERBST, Primary Examiner.

1. A FORMING HEAD MECHANISM FOR ELECTRO-HYDRAULICALLY SHAPING A DRAWNCUP-SHAPED CONTAINER BODY IN A FORMING DIE COMPRISING A SUPPORT, ATUBULAR IMPERMEABLE RUBBER DIAPHRAGM SECURED AT ONE END TO SAID SUPPORTIN FLUID TIGHT ENGAGEMENT, SAID DIAPHRAGM HAVING EXTERIOR GEOMETRYSUBSTANTIALLY THE SAME AS THE INTERIOR OF SAID BODY AND BEING INSERTIBLETHEREIN, A PAIR OF ELECTRODES TIGHTLY INSERTED WITHIN THE OPPOSITE ENDSOF SAID DIAPHRAGM WITH THEIR TIPS PROJECTING INWARDLY OF SAID ENDS INPREDETERMINED SPACED ALIGNMENT, ONE OF SAID ELECTRODES EXTENDING THROUGHSAID SUPPORT AND THE OTHER BEING SECURED IN FLUID TIGHT ENGAGEMENT TOTHE OPPOSITE END OF SAID DIAPHRAGM, SAID OTHER ELECTRODE HAVING ANEXTERIOR CONTACTING FACE CONTOURED TO CONFORM SUBSTANTIALLY TO THECLOSED END OF SAID CUP-SHAPED BODY WHEN SAID DIAPHRAGM IS INSERTEDTHEREIN TO MAKE ELECTRICAL CONTACT THROUGH SAID END PANEL WITH THECONDUCTOR OF AN ELECTRICAL POWER SOURCE ADAPTED